experiments: Make sure memcached is killed properly

experiments/memcached.shared.sh

@@ -10,7 +10,9 @@ cleanup_mutilate() {
 
 cleanup_memcached() {
     echo "Killing memcached process"
-    kill -INT $MEMCACHED_PID
+    kill -INT $MEMCACHED_PID || true
+    sleep 2
+    kill $MEMCACHED_PID || true
 }
 
 start_memcached() {